1. Field of the Invention
This invention relates to a vehicle body structure. More specifically, the present invention relates to a vehicle body structure for reducing an impact of occupants in a vehicle during a side collision.
2. Background Information
A vehicle body structure typically has one or more swingably mounted doors that latch to a center pillar. The upper and the lower ends of the center pillar are welded to a side roof rail and a side sill, respectively. The cross section of the center pillar is formed with a closed cross section over its entire length between the side roof rail and the side sill. When another vehicle collides with the side of a vehicle having this type of side structure, the center pillar and the front and rear doors of the vehicle are compressed by the front portion of the colliding vehicle. More specifically, the center pillar or structural member tends to bend at the center towards the occupant. Since the height of the center portion of the center pillar or structural member is located at almost the same height of the chest of an occupant, the occupant's chest may contact the center portion of the center pillar or structural member.
One attempt to solve this phenomenon is disclosed in Japanese Laid-Open Patent Application No. 8-72740. This publication discloses a side structure of a vehicle having a center pillar or structural member that is formed with a closed cross section over its entirety. The center pillar has a strength-discontinuity portion formed at a lower portion of the center pillar. When another vehicle collides against the side of a vehicle having this type of structure, the center or structural member is bent at the strength-discontinuity portion and the upper portion of the center pillar is moved horizontally with respect to the vehicle cabin. Accordingly, the contact degree with occupant and the center pillar will relatively be reduced.
As mentioned above, in conventional vehicle body structures, an improvement is applied merely to the structure of a center pillar itself.
In actual side collision cases, however, the front portion of a colliding vehicle hits not only the center pillar but also one or both doors of the vehicle and compresses one or both of the doors. In particular, the center pillar is made of a frame material having a closed cross section that is relatively strong against a bending moment generated during a side collision. The door, on the other hand, generally has a weaker strength than center pillar against an external surface force generated during a side collision, since the door is made of a paneling material with many openings. Accordingly, the front portion of the colliding vehicle tends to be deformed so as to surround the center pillar. Thus, the door moves farther into the cabin of the vehicle as compared with the center pillar. If the door is moved more towards the interior of the vehicle relative to the center pillar or structural member, as mentioned above, the door pulls the center pillar via an engaging mechanism, which results in deformation of the center pillar. Conventionally, this deformation is controlled by increasing the thickness of a door panel or other reinforcement parts. Accordingly, although the above-mentioned deformation of the center pillar will be avoided by using conventional technique, there is a disadvantage in the increase of weight.
Also, although an energy absorbing member for relieving an impact is often provided with doors as a measure for side collision, the size of the energy absorbing member has to be very large to provide good impact absorption. Specifically, in cases where the door and the center pillar are strongly bound, if the capacity of the energy absorbing member is relatively small, deformation of the energy absorbing member may be over or almost over before the door contacts an occupant. Accordingly, there is a disadvantage in prior art in that the width of a vehicle may be significantly increased.
Moreover, Japanese Laid-Open Patent Application No. 10-196183 discloses a door lock that is released upon a side collision. The release mechanism of this publication simply releases the door lock. However, the latch of the door is still engaged with a striker on the center pillar. Therefore, the load applied to the door is transmitted to the center pillar and the above-mentioned problem is not solved by this technique.
In view of the above, there exists a need for a vehicle body side structure which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.